Absolute acceleration sensor for use within moving vehicles

ABSTRACT

A method of and system for detecting absolute acceleration along various axes relative to a desired movement vector while moving relative to a gravity source includes steps of determining a vertical acceleration, perpendicular to the desired movement vector and substantially anti-parallel to a gravitational acceleration due to the gravity source; determining a longitudinal acceleration, parallel to the desired movement vector and to output at vertical acceleration signal and a longitudinal acceleration signal; determining an inclination of the desired movement vector relative to the gravitational acceleration; and processing the vertical acceleration signal, the longitudinal acceleration signal, and the inclination signal to produce an absolute vertical acceleration signal and an absolute longitudinal acceleration signal.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/243,364, filed on Oct. 3, 2005, now U.S. Pat. No. 7,239,953 andentitled “ABSOLUTE ACCELERATION SENSOR FOR USE WITHIN MOVING VEHICLES”which claims priority under 35 U.S.C. 119(e) of the U.S. provisionalpatent application, Application No. 60/616,400, filed on Oct. 5, 2004,and entitled “REAR-END COLLISION AVOIDANCE SYSTEM.” The U.S. patentapplication Ser. No. 11/243,364, filed on Oct. 3, 2005, and entitled“ABSOLUTE ACCELERATION SENSOR FOR USE WITHIN MOVING VEHICLES” and theprovisional patent application, Application No. 60/616,400, filed onOct. 5, 2004, and entitled “REAR-END COLLISION AVOIDANCE SYSTEM” arealso hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to methods and devices fordetecting absolute levels of longitudinal, lateral and verticalacceleration within moving vehicles, and to a variety of systems andmethods for generating responses to changes in these absolute levels.

BACKGROUND OF THE INVENTION

Accelerometers find a wide variety of applications within modern motorvehicles. The most common of these are impact and collision sensors usedto deploy front and side impact air bags in modern passenger cars andtrucks.

In applications that depend on sudden and drastic deceleration, thepresence of gravity is of little consequence and will not affect theimplementation of the accelerometer. However, increasingly feedbacksystems within motor vehicles have attempted to make use ofaccelerometer data during much lower and subtler levels of acceleration.

One example is anti-collision warning systems. Though all street legalmotor vehicles have brake lamps configured to signal other drivers ofbraking, these signals do not warn following drivers of imminentbraking. At least one system has proposed activating a vehicle's brakelamp system in response to a deceleration signal from a sensitiveaccelerometer, and independent of actuation of the brake pedal. Thesystem described in U.S. Pat. No. 6,411,204 to Bloomfield et al.,entitled “DECELERATION BASED ANTI-COLLISION SAFETY LIGHT CONTROL FORVEHICLE,” includes a plurality of deceleration thresholds each with anassociated modulation of the brake lamps.

However, the system fails to precisely account for gravitational forces,limiting its effectiveness to deceleration regimes where gravity'seffect is minimal and reducing its effectiveness as an early warningsystem. Accelerometers, known as tilt sensors in the gaming and roboticsindustries, are extremely sensitive to any gravitational force to whichthey are not perpendicular. This sensitivity complicates any system thatattempts to detect low levels of acceleration by using accelerometerswithin moving vehicles, since the system must account for the widevariety of orientations of the accelerometer relative to the earth'sgravity introduced as the vehicle travels uphill, downhill, throughcambered or off-camber curves, and on cambered grades. For instance, anaccelerometer in a vehicle stopped on a 45-degree downhill slope wouldsense deceleration of a magnitude equal to 0.71 times the accelerationdue to gravity. To avoid gravitational acceleration artifacts, thesystem of Bloomfield only produces output if the deceleration signalrises above a predetermined threshold set above the level of artifactsintroduced during typical driving conditions.

However, the reliance of this device on a threshold deceleration reducesits effectiveness as an early warning system. Even a short delay betweenthe time when the subject vehicle begins to slow down and the time whena following vehicle begins to slow can result in a rapid closure of thegap, or following distance, between the vehicles, and a potentialcollision. Consequently, the shorter the following distance betweenvehicles, the smaller the margin of error will be for drivers offollowing vehicles to avoid rear-end collisions. Disengaging theaccelerator, or coasting, is often the first response of the driver of asubject vehicle to observing a non-urgent traffic event in the roadwayahead, and usually results in a slight deceleration. By failing to warnother drivers of the possible imminence of braking of a subject vehicle,the proposed device loses valuable time. To avoid this problem, thethreshold must be set lower, which could result in gravitationalacceleration artifacts affecting the system's output. For example, anoverly low threshold could prevent the device from signalingdeceleration on an uphill grade since the accelerometer would sense acomponent of the earth's gravity as acceleration. Similarly, a lowthreshold could cause the device to continuously flash during a descent,while gravity appears as deceleration.

The loss of time incurred by a threshold-based system might be tolerablein some other application; but in collision prevention, even an instantsaved can prevent a collision. A Special Investigative Report issued inJanuary of 2001 by the National Transportation Safety Board (NTSB)illustrates the scale of the problem. The report notes that in 1999“1.848 Million rear-end collisions on US roads kill[ed] thousands andinjur[ed] approximately [one] Million people.” The report concluded thateven a slightly earlier warning could prevent many rear-end collisions.

-   -   Regardless of the individual circumstances, the drivers in these        accidents were unable to detect slowed or stopped traffic and to        stop their vehicles in time to prevent a rear-end collision. If        passenger car drivers have a 0.5-second additional warning time,        about 60 percent of rear-end collisions can be prevented. An        extra second of warning time can prevent about 90 percent of        rear-end collisions. [NTSB Special Investigative Report        SIR—January 2001, Vehicle-and Infrastructure-based Technology        for the Prevention of Rear-end Collisions]

SUMMARY OF THE INVENTION

In this application “acceleration” refers to either or both positiveacceleration and negative acceleration (sometimes called“deceleration”), while “deceleration” refers to only negativeacceleration.

The present invention relates to devices that overcome the limitationsof the prior art by integrating signals from two separate sensors thathave completely different references to construct a signal representingonly actual acceleration, including deceleration, of the vehicle. Thepreferred embodiments use signals from both an accelerometer, whichsometimes detects gravitational acceleration in addition to actualvehicle acceleration, and a gyroscope configured to sense deviationsfrom the plane perpendicular to the earth's gravity. By modifying thesignals from the accelerometer based on those from the gyroscope, thepreferred embodiments monitor the absolute acceleration, includingabsolute deceleration, of the vehicle relative to the road.

The preferred embodiment of the present invention combines an integratedaccelerometer and an integrated gyroscope, such as a rate gyroscope, ina single system that electronically integrates their signals to providefor highly accurate detection of absolute acceleration with no arbitrarythresholds required. Elsewhere, this portion of the present invention isreferred to as an “accelerometer-g-sensor.”

In one aspect, the present invention relates to a method of detectingabsolute acceleration along various axes relative to a movement vectorwhile moving relative to a gravity source, comprising: determining avertical acceleration, perpendicular to the movement vector andsubstantially anti-parallel to a gravitational acceleration due to thegravity source; determining a longitudinal acceleration, parallel to themovement vector and to output a vertical acceleration signal and alongitudinal acceleration signal; determining an inclination of themovement vector relative to the gravitational acceleration; andprocessing the vertical acceleration signal, the longitudinalacceleration signal, and the inclination signal to produce an absolutevertical acceleration signal and an absolute longitudinal accelerationsignal.

In another aspect, the invention relates to a system for detectingabsolute acceleration along various axes relative to a movement vectorwhile moving relative to a gravity source, comprising: a two-axisaccelerometer configured to sense both a vertical acceleration,perpendicular to the movement vector and substantially anti-parallel toa gravitational acceleration due to the gravity source, and alongitudinal acceleration, parallel to the movement vector and to outputa vertical acceleration signal and a longitudinal acceleration signal; agyroscope configured to sense an inclination of the movement vectorrelative to the gravitational acceleration and to output an inclinationsignal; and a logic circuit configured to process the verticalacceleration signal, the longitudinal acceleration signal, and theinclination signal to produce an absolute vertical acceleration signaland an absolute longitudinal acceleration signal.

Rear End Collision

The present invention provides systems and methods for warning driversof other vehicles of any possibility that a subject vehicle will brakeand/or that the following vehicle may need to decelerate. This warningoccurs earlier than warnings provided by traditional rear brake warningsystems. The preferred embodiment of the present invention takesadvantage of the existing conditioning of modern drivers to respondquickly to rear brake warning lamps by using these systems to convey newdeceleration warnings. In one aspect, the present invention relates to acommunication system for a vehicle. The communication system includes anabsolute deceleration detector including an accelerometer, a gyroscope,and a control logic and configured to detect an absolute decelerationstatus of the vehicle, a braking system engagement detector to detect abraking status of the vehicle, an alerting device capable of signalingother drivers of a deceleration condition of the vehicle, and a controldevice coupled to the accelerometer-gyroscopic sensor, the throttleengagement detector, the braking system engagement detector, and thealerting device. In this configuration, the accelerometer-gyroscopicsensor sends signals to the control device and the control deviceoperates the alerting device in a manner dependent on the decelerationstatus, the braking status, and the throttle status of the vehicle.

In another aspect, the present invention describes a method of alertingdrivers in proximity to a vehicle of deceleration and braking of thevehicle. The method includes steps of sensing an apparent rate ofdeceleration of the vehicle, sensing an inclination of the vehiclerelative to a gravitational acceleration, correcting the apparent rateof deceleration to account for an effect of gravitational accelerationto determine an absolute rate of deceleration of the vehicle, detectinga braking status of the vehicle, and emitting a signal to indicate thatthe vehicle is decelerating. In this aspect, the signal varies dependingon the rate of deceleration, the braking status, and the throttle statusof the vehicle.

In a third aspect, the present invention relates to a method of forminga communication system for a vehicle. The method comprises a step ofadding a deceleration warning circuit to a brake lamp system of thevehicle coupled with the deceleration detection circuit. In this method,the deceleration detection circuit comprises a deceleration detector,wherein the deceleration detector detects any deceleration of thevehicle, a gyroscope, wherein the gyroscope detects an inclination ofthe vehicle relative to a gravitational acceleration, a logic circuitconfigured to determine an absolute deceleration from the decelerationof the vehicle and the inclination of the vehicle, a braking systemengagement detector, wherein the braking system engagement detector anyengagement of a braking system of the vehicle, wherein the throttleengagement detector detects any disengagement of a throttle of thevehicle, and a control device coupled to the accelerometer-gyroscopicsensor and the braking system engagement detector, wherein theaccelerometer-gyroscopic sensor, the braking system engagement detector,and the throttle engagement detector send signals to the control device,and wherein the control device activates brake lamps of the vehicle ifthe throttle is disengaged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a single axis accelerometer positioned for measuringlateral acceleration, and included in an accelerometer-gyroscopic sensorin accordance with an embodiment of the present invention.

FIG. 1B illustrates a dual axis accelerometer positioned for measuringvertical and longitudinal acceleration, and included in anaccelerometer-gyroscopic sensor in accordance with an embodiment of thepresent invention.

FIG. 2A illustrates a gyroscope positioned for measuring a heading, andincluded in an accelerometer-gyroscopic sensor in accordance with anembodiment of the present invention.

FIG. 2B illustrates a gyroscope positioned for measuring a lateralinclination, and included in an accelerometer-gyroscopic sensor inaccordance with an embodiment of the present invention.

FIG. 2C illustrates a longitudinal inclination, and included in anaccelerometer-gyroscopic sensor in accordance with an embodiment of thepresent invention.

FIG. 3A is a schematic view illustrating the components of the rear-endcollision avoidance system, warning drivers of a subject vehicle'sdeceleration, in accordance with an embodiment of the present invention.

FIG. 3B illustrates a state machine diagram of the control device inaccordance with the preferred embodiment of the present invention.

FIG. 3C illustrates a state machine diagram of the control device inaccordance with an alternative embodiment of the present invention.

FIG. 4 illustrates a schematic view of an anti-rollover system inaccordance with an embodiment of the present invention.

FIG. 5 illustrates a schematic view of an engine performance monitoringsystem in accordance with an embodiment of the present invention.

FIG. 6 illustrates a schematic view of a suspension and road conditionmonitoring system in accordance with an embodiment of the presentinvention.

FIG. 7 illustrates a navigation system in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes systems and methods for detectingabsolute rates of acceleration of bodies moving relative to agravitational acceleration. The preferred embodiment uses signals fromboth an accelerometer, which sometimes detects gravitationalacceleration in addition to actual vehicle acceleration, and agyroscope, which can sense deviations from the plane perpendicular toearth's gravity. By modifying the signals from the accelerometer basedon those from the gyroscope, the preferred embodiment monitors theabsolute acceleration or deceleration of a vehicle relative to the road,or some other body relative to any object that is fixed relative to somegravity source that affects the body.

As shown in FIGS. 1B and 2C, the preferred embodiment of the presentinvention includes a dual axis accelerometer and an electronic gyroscopepositioned upon a moving body (not shown) having a pitch axis and a yawaxis that form a pitch-yaw plane as illustrated, which attempts to movealong a movement vector orthogonal to the pitch-yaw plane. A first axis,termed the longitudinal axis, of the dual axis accelerometer is placedorthogonal to the plane of the pitch and yaw axes to sense accelerationalong the movement vector. A second axis, termed the vertical axis, ofthe accelerometer is placed parallel with the yaw axis (and thusperpendicular to the movement vector) to sense acceleration along theyaw axis. Thus the two axes of the accelerometer form alongitudinal-vertical plane orthogonal to the pitch-yaw plane.

The gyroscope in FIG. 2C is mounted parallel to thelongitudinal-vertical plane of the accelerometer and thus is also alonga plane perpendicular to the pitch-yaw plane of the moving body. Thisconfiguration allows it to sense an inclination of the movement vectorof the moving body relative to the gravitational acceleration acting onthe body.

In some embodiments of the present invention, additional gyroscopes andaccelerometers are mounted on the moving body at other orientations.Output from these additional sensors is useful for anti-roll suspensionadjustment, among other things. The orientations shown in FIGS. 1A and2B allow for detection of lateral acceleration and inclination. In FIG.1A, a single axis accelerometer configured with a first axis, termed thelateral axis, parallel to the pitch axis senses lateral acceleration ofthe body, e.g. acceleration in a plane orthogonal to thelongitudinal-vertical plane.

When the body does undergo a lateral acceleration, its actual movementis no longer along the desired movement vector. Thus, during lateralacceleration, another gyroscope must be included to sense theinclination of the component of the actual movement vector that liesalong the lateral axis. FIG. 2B depicts a gyroscope configured parallelto the pitch-yaw plane and thus configured to detect an inclination ofthe component of movement that lies along the lateral axis, termed thelateral inclination of the body.

In some embodiments, the system also includes another gyroscope that isconfigured parallel to the lateral-longitudinal plane (in which alldesirable movement vectors will lie), to detect a heading of the body.This additional gyroscope is required for those embodiments that supplysupplemental data to navigation systems.

Preferably, the embodiments of the present invention include logiccircuits configured to receive signals of acceleration along thelateral, longitudinal, and vertical axes, as well as of the lateral andlongitudinal inclinations and the heading, and to process these signalsto produce a variety of output signals indicating characteristics of themoving body's movement. These preferably include: absolute longitudinalacceleration (both positive and negative), absolute verticalacceleration (both positive and negative), absolute lateral acceleration(both positive and negative), heading, and actual speed.

Though accelerometers are inherently stable, and especially so wheninternally temperature compensated, gyroscopes, both mechanical andelectronic, can suffer from instability and drift. Because of thesedrift characteristics, gyroscopes typically require periodicauto-zeroing or re-referencing to provide reliable output.

In some embodiments of the present invention, a method of detecting anabsolute deceleration includes steps of re-referencing. This task ispreferably accomplished using signals from the accelerometers, but inother embodiments use a Hall effect, electronic or other type ofcompass.

Re-referencing preferably takes place periodically; for systems usingHall effect or some other independent compass, the systems simplyre-reference at specified heading or timing intervals. However, systemsthat use accelerometer data for re-referencing are preferably morecareful. When stationary, any signal from the accelerometer isessentially representative of the earth's gravity, this signal canprovide an initial reference for any gyroscopes included in the presentinvention, which preferably takes place prior to movement of the body.

Once the body has begun moving, without periodic re-referencing, thegyroscope output can become unreliable. The present invention teachesseveral methods of re-referencing during travel. Some of these are onlyapplicable to travel that includes periodic stops. For example, thevertical or lateral axis accelerometers can be used to detect whetherthe body is stopped. When it is stopped, the signal from thelongitudinal axis of the accelerometer can be used to re-reference thegyroscope. Further, at any point during travel when no acceleration hasbeen detected for a predetermined period of time the gyroscope can bere-referenced. In this way repeated referencing can occur even duringextended travel without any stops.

The present invention is preferably implemented in a vehicle, and thefollowing embodiments of the present invention are described relative toa vehicle. However, the methods and systems taught by the presentinvention can be implemented in a wide variety of moving bodies otherthan vehicles. Further, for convenience, the devices described abovewith reference to FIGS. 1A, 1B, 2A, 2B, and 2C are termed an“accelerometer-gyroscopic sensor” when referenced elsewhere.

Example 1 Rear End Collision Avoidance

FIG. 3A is a schematic view illustrating the components of the rear-endcollision avoidance system 300, warning drivers of a subject vehicle'sdeceleration, in accordance with one embodiment of the presentinvention. The rear-end collision avoidance system 300 comprises anaccelerometer-gyroscopic sensor 310, a braking system engagementdetector 320, a throttle engagement detector 330, and a control device340. The accelerometer-gyroscopic sensor 310 is coupled to the controldevice 340, detects an absolute longitudinal deceleration of thevehicle, and sends a signal to the control device 340. The brakingsystem engagement detector 320 is also coupled to the control device340, detects any engagement of the braking system of the vehicle, andsends a signal to the control device 340. The throttle engagementdetector 330 is also coupled to the control device 340 and detectsengagement of the throttle. In alternative embodiments, the presentinvention also includes additional input devices, such as a clutchengagement detector configured to relay a clutch status to the controldevice 340. Next, the control device 340 processes the input signals itreceives from the accelerometer-gyroscopic sensor 310, the brakingsystem engagement detector 320, and the throttle engagement detector 330and decides whether to activate an alerting device of the vehicle. Insome embodiment the control device 340 only activates an alerting deviceif the vehicle is throttled down but not braking. In some embodiments,the control device 340 activates the alerting device only if theabsolute longitudinal deceleration is non-zero. In one embodiment, thecommunication system further comprises an alerting device activationcircuit 350, wherein the control device 340 is coupled to and sendssignals to the alerting device activation circuit 350, which activatesan alerting device based on a signal from the control device 340.

The embodiments of the present invention include input devices. Thosementioned above include braking system engagement detectors, throttleengagement detectors, and the accelerometer-gyroscopic sensor. Inalternative embodiments, the present invention also includes additionalinput devices, such as a clutch engagement detector configured to relaya clutch status to the control device.

The embodiments of the present invention include alerting devices. Inthe present invention, an alerting device preferably comprises lamps onthe vehicle that are capable of flashing and emitting visible light. Inone aspect, the lamps of the alerting device flash only at a constantrate, while in another aspect the lamps flash at a variable rate, andfurther wherein the control device is configured to flash the lamps at arate correlated to a rate of deceleration. The lamps are preferably oneof the following: conventional signaling lamps and conventional brakelamps. However, in another embodiment, the alerting device is a radiofrequency (RF) transmitter capable of directing RF signals from the rearof the vehicle to a following vehicle. In other embodiments, thealerting device uses other types of signals.

When used in this patent, the terms “conventional signaling lamps” and“conventional brake lamps” refer to signaling or brake lamps included onmotor vehicles during their original manufacture. The present inventionalso contemplates signaling by using after-market devices that areattached to a vehicle in addition to conventional signaling and brakelamps.

A communication system can be embodied as an after-market add-on productor as an original vehicle system. These embodiments include differenttypes of controllers. In an add-on system, a control device preferablydoes not interfere with the existing brake lamp system controller. Thecontrol device communicates with the brake lamps in a substantiallyseparate manner from the existing brake lamp control system. Controldevices used in the present invention could include relays, switches ormicro controllers. In one aspect, an aftermarket system can continuouslypower the alerting device activation circuit without need of anintermediate control device.

However, in an original equipment system, a communication system inaccordance with the present invention preferably includes a controldevice that further comprises a control system for the conventionalbrake lamp system, whereby the communication system is an integratedcontrol and circuitry system for all brake lamps. In this aspect, asingle control system accomplishes the tasks of conventional brakesignaling and the signaling described in the present invention.

During operation, the communications system of the present inventionuses information from the various input devices to determine a manner inwhich to operate an alerting device. In one aspect, the communicationssystem continuously modulates the alerting device based on theaccelerometer-gyroscopic sensor's input so long as the throttle isdisengaged, regardless of braking system status. In another aspect, oncethe braking system is engaged, the communications system activates thealerting device continuously until disengagement of the braking system,whereupon the communications system once again considers throttle andthe accelerometer-gyroscopic sensor's input in choosing a manner inwhich to operate the alerting device. In a third aspect, where aconventional braking system exists separately from a communicationssystem as described in the present invention, the control devicedeactivates in response to braking system engagement and reactivatesupon braking system disengagement. Preferably, the control devicereceives input in cycles and makes a determination for operation of thealerting device within each cycle.

In one embodiment, the control device 340 takes input from theaccelerometer-gyroscopic sensor 310, the braking system engagementdetector 320, and the throttle engagement detector 330 in cycles thatare substantially continuous in time. In the preferred embodiment, foreach cycle, the control device 340 enters one of four states: I) it doesnot activate an alerting device for the entirety of the cycle, II) itactivates an alerting device for the entirety of the cycle, III) itactivates an alerting device at least once for a period of time that isshort relative to the duration of the cycle; or IV) it activates analerting device multiple times during the cycle.

FIG. 3B illustrates a preferred embodiment in which these four outputstates are handled. A state machine 301, included in a control device inaccordance with the present invention, takes five possible input states,for four of them throttle status is not considered: 1) brake pedal isnot depressed, absolute deceleration is not detected; 2) brake pedal isnot depressed, absolute deceleration is detected; 3) brake pedal isdepressed, absolute deceleration is detected; or 4) brake pedal isdepressed, absolute deceleration is not detected. State 5) only occursif the throttle is disengaged, and if the brake pedal is not depressed.Input state 1 corresponds to output state I, input state 2 correspondsto output state III, input states 3 and 5 correspond to output state II,and input state 4 corresponds to output state IV.

Transitions between all input states are handled and every transition isa plausible outcome of a braking or acceleration event. For example, adriver disengaging the throttle pedal causes a transition from state 1to state 5. In the first cycle detecting state 5, the brake lamps areilluminated. Once a required level of absolute deceleration is detected,a transition from state 5 to state 2 occurs. In the first cycledetecting state 2, the brake lamps are flashed, or another alertingdevice is activated, corresponding to output state III. A transitionfrom state 1 directly to state 2 can occur when beginning ascent of asteep grade: the throttle is engaged, the brake pedal is disengaged butthe vehicle begins to decelerate.

If the driver engages the throttle again, or in the case of an ascent,increases the throttle, a transition from state 5 to state 1, or state 2to state 1, occurs. If the driver subsequently depresses the brakepedal, a transition from state 2, or state 5, to state 3 occurs. Whilethe brake pedal is depressed, state II output keeps the brake lampsilluminated. Furthermore, while the brake pedal is depressed, atransition from state 3 to state 4 may occur. In this embodiment, instate 4 the lamps are flashed at an increased rate. Whenever the brakepedal is depressed, state II or IV output occurs andaccelerometer-gyroscopic sensor data is effectively ignored. When thebrake pedal is released, one of input state 1, input state 2, and inputstate 5 are entered.

A transition from input state 3 to 2 corresponds to tapping or pumpingthe brake pedal. Depending on the length of time a cycle comprises, aresidual brake lamp flash may occur. Transitions from input states 3 or4 to state 1 correspond respectively to accelerating from a rolling stopon a hill, or rolling forward downhill. A transition from input state 4to 2 could arise when rolling down a hill backwards, for example at astoplight on a hill. This points to another feature of the currentsystem—providing a warning for rollback.

In the alternative embodiment illustrated in FIG. 3C, a state machine301′ included in a control device in accordance with the presentinvention, the system only considers the first three states. The statemachine 301′ takes four possible input states: 1) brake pedal is notdepressed, absolute deceleration is not detected; 2) brake pedal is notdepressed, absolute deceleration is detected; 3) brake pedal isdepressed, absolute deceleration is detected; or 4) brake pedal isdepressed, absolute deceleration is not detected. Input state 1corresponds to output state I, input state 2 corresponds to output stateIII, and input states 3 and 4 correspond to output state II.

Transitions between all input states are handled and every transition isa plausible outcome of a braking or acceleration event. For example, adriver taking his or her foot off the accelerator pedal causes atransition from state 1 to state 2. In the first cycle detecting state2, the brake lamps are flashed, or other alerting means are activated,corresponding to output state III. This transition from state 1 to state2 also occurs when beginning ascent of a steep grade: the accelerator isdepressed, the brake pedal is disengaged but the vehicle begins todecelerate. If the driver presses the accelerator again, or in the caseof an ascent, further depresses the accelerator, a transition from state2 to state 1 occurs. If the driver subsequently depresses the brakepedal, a transition from state 2 to state 3 occurs. While the brakepedal is depressed, state II output keeps the brake lamps illuminated.Furthermore, while the brake pedal is depressed, a transition from state3 to state 4 may occur. In this embodiment, such a transition results inno change in output. Whenever the brake pedal is depressed, state IIoutput occurs and accelerometer-gyroscopic sensor data is effectivelyignored. When the brake pedal is released, either input state 1 or inputstate 2 is entered.

Transitions between states in this embodiment are similar to those inthe preferred embodiment. A transition from input state 3 to 2corresponds to tapping or pumping the brake pedal. Depending on thelength of time a cycle comprises, a residual brake lamp flash may occur.Transitions from input states 3 or 4 to state 1 correspond respectivelyto accelerating from a rolling stop on a hill, or rolling forwarddownhill. A transition from input state 4 to 2 could arise when rollingdown a hill backwards, for example at a stoplight on a hill. This pointsto another feature of the current system—providing a warning forrollback.

Embodiments of the present invention provide the driver of a subjectvehicle a communication system that provides warning signals to othervehicles of any absolute deceleration or possibility of braking of thesubject vehicle. One novel and distinguishing feature of this inventionis that the subject vehicle's communication system warns other vehiclesof any possibility that the subject vehicle will begin to brake. This isso because any engagement of the brake pedal is usually immediatelypreceded by a disengagement of the throttle.

Thus, this invention provides an earlier warning to the driver of thefollowing vehicle of a subject vehicle's intent to decelerate than iscurrently available in modern vehicles, which only provide systems thatactuate warning lamps if the driver depresses the brake pedal or if anaccelerometer unit detects a threshold deceleration. Modern driversrespond quickly to rear brake warning lamps, conditioning that thepresent invention takes advantage of by using these warning systems toconvey new and broader warnings. Since following distances on modernroadways are often inadequate, this arrangement could prevent numerousrear-end collisions.

Example 2 Anti-Rollover Systems

In one embodiment of this invention, outputs from the sensing ofabsolute lateral acceleration are used to adjust suspension systems bystiffening outside suspension and/or loosening inside suspension ofmoving vehicles. When lateral acceleration or force is applied to avehicle, it tends to lean in the direction opposite to the force beingapplied, due in part to the softness of their suspension systems. Thismoves the center of gravity further off center and in some cases outsideof their wheelbase approaching the critical rollover point. Stiffeningthe outside suspension and/or loosening the inside suspension keeps thecenter of gravity of vehicles within a tighter envelope relative to thewheelbase. This inversely affects the propensity, especially in highcenter of gravity loaded vehicles, to rollover when the center ofgravity of their load exceeds the wheelbase and reaches the criticalrollover point. Additionally, by adjusting the suspension system in thismanner the distribution of load between left and right side wheels iskept more even resulting in improved traction.

Typically these are configured as pulse width modulated (PWM)controlling devices. Such devices typically accept analog voltage levelinputs, which are then converted to a corresponding pulse width output.Such outputs are a common method of controlling and delivering aregulated amount of current to a device such as a hydraulic solenoid.The hydraulic solenoids of course are responsible for increasing,decreasing or maintaining pressure levels within the hydraulic orpneumatic suspension system.

An anti-rollover device 400 is illustrated in FIG. 4. In this embodimentvehicles are assumed to be equipped with adjustable suspension systems,typically hydraulic or pneumatic. When absolute lateral acceleration issensed the accelerometer-gyroscopic sensor 410 sends a signalrepresenting absolute lateral acceleration to a suspension selector 420,which passes signals along to a controller responsible for controllingthe relevant quadrant of the suspension. The suspension selector 420must interpret the signal to determine the appropriate quadrant. Forexample, Q1, in which suspension system 432 is controlled by suspensioncontrol 431 could be the right front wheel; Q2, in which suspensionsystem 442 is controlled by suspension control 441 could be the leftfront wheel; Q3, in which suspension system 452 is controlled bysuspension control 451 could be the right rear wheel; and Q4, in whichsuspension system 462 is controlled by suspension control 461 could bethe left rear wheel. Of course, other orderings are possible, as aresystems with only two independent zones, e.g. two sides are controlledin lockstep.

Example 3 Performance Monitoring Systems

Due to fuel efficiency goals and competitive pressures late modelvehicles have the ability to monitor engine system performance throughan array of sensors and detectors. The absolute accelerometer/gyroscopecombination provides the ability to communicate actualpower-to-the-ground data for use in engine/vehicle performancecomputations. In this embodiment, the accelerometer-gyroscopic sensorcontinuously sums absolute acceleration values to provide both absoluteacceleration and actual speed values, which can be used by amanufacturers vehicle computer unit (VCU).

For example, the system 500 shown in FIG. 5 includes theaccelerometer-gyroscopic sensor 510, which delivers actual speed dataand absolute acceleration data to a vehicle computer unit (VCU) 520 (orat least the engine monitoring portion thereof). The VCU 520 usesbaseline engine performance data 540 to either self-correct through afeedback mechanism, or to issue a warning through the performancewarning system.

The manufacturer's baseline engine performance data is helpful indetermining how much acceleration should be achieved for a given amountof throttle and what the speed of the vehicle should be for a givenamount of throttle. For instance, a VCU may have tuned to maximumefficiency however the vehicle's corresponding speed or acceleration maybe many percentage points less than what would be expected, indicatingperhaps that the tire pressure is low or that the vehicle is loaded to ahigher level than what would be normal, in which case the tire pressureshould be increased.

Example 4 Road or Suspension Condition Monitoring Systems

Because an accelerometer-gyroscopic sensor, which is used and is part ofthis invention can use one axis of a dual axis accelerometer in thevertical position vertical acceleration output signals are madeavailable to other monitors or computers that require this information.Such a requirement may be to monitor and evaluate road quality and/orshock absorber utilization and performance. For instance, it is apparentto a rider in a vehicle when such vehicle is riding on worn out shockabsorbers. However, it becomes less apparent when those shock absorberswear out slowly over an extended period of time. The first time a drivermay realize that shock absorbers have worn out is in cases wherecritical performance is required. Or when they replace worn out tiresand see the evidence on tires of worn out shock absorbers. The absoluteA/G sensor detects vertical acceleration in very small increments.Increasing levels of vertical acceleration can easily be monitored thusproviding notice to drivers of the degradation of shock absorber system.

For example, in the system 600 shown in FIG. 6, theaccelerometer-gyroscopic sensor 610 provides absolute verticalacceleration data to a VCU 620 or at least a suspension-monitoringportion thereof. The VCU 620 can use baseline suspension performancedata 640 to either self-correct through a feedback mechanism or issue awarning through the suspension warning system 630.

Example 5 Navigation Systems

In most embodiments, the accelerometer-gyroscopic sensor is continuouslymonitoring acceleration; a unit of acceleration multiplied by a unit oftime yields a unit of velocity (with speed as its magnitude).Preferably, the accelerometer-gyroscopic sensor continuously sums unitsof acceleration over small increments of time. In this case, theaccelerometer-gyroscopic sensor provides the integrated velocity orspeed as an output. Preferably, when a horizontally mounted gyroscope isincorporated, the accelerometer-gyroscopic sensor also providesdirection or heading as an output.

Because velocity, or speed and heading are the raw elements required forinertial navigation systems. In the system 700 shown in FIG. 7, theaccelerometer-gyroscopic sensor 710 provides actual speed and headinginformation as an output to a navigation system controller 720. Thenavigation system controller 720, which normally provides navigationdata from a global positioning system (GPS) 730 directly to thenavigation system input/output (I/O) 750, incorporates headinginformation from the accelerometer-gyroscopic sensor 710 during periodsof connection loss with the GPS satellite system. In return forproviding the heading data to the inertial navigation system 740, thenavigation controller receives navigation data from the inertial systemto supplement or replace its GPS data.

Preferably, the navigation system controller 720 also provides GPSheading data back to the accelerometer-gyroscopic sensor 710 to permitre-referencing of the gyroscopes contained therein. Continuousreferencing and re-referencing of the horizontally mounted gyroscopeutilize GPS heading values while satellite signals are acquired. Oncesatellite signals are lost gyroscopic heading values take priority usinglast known valid headings from the GPS. This method using absolute A/Gvalues for supplementing data to the GPS data when the GPS system haslost signal will find use in many applications outside of the automotiveindustry.

These elements in output signal format are made available to on boardGPS based navigation systems through a data port for supplementationduring periods of lost or down satellite signals so that the user of aGPS navigation system sees no down time during these periods.

In another aspect, since speed or velocity can be tracked by summingpositive and negative accelerations and multiplying by time, a secondmultiplication by time can yield distance, which is also useful innavigation.

Example 6 Altimeter Systems

In another aspect, summing positive and negative vertical accelerationsover time yields altitude. For example, an instrument, including anaccelerometer-gyroscopic sensor, placed in an airplane or other flyingobject, contains a circuit that continuously sums over all accelerationsand outputs altitude. Alternatively, a system including anaccelerometer-gyroscopic sensor included in a non-flying vehicle trackschanges in altitude and outputs a signal used to vary engine performanceor some other type of parameter.

This method of altitude determination has certain advantages overcurrent methods of determining altitude which rely on either radar,pressure sensors, or GPS triangulation. Of course its accuracy indetermining altitude above sea level (ASL) relies on knowledge ofinitial altitude, and its accuracy in determining altitude above groundlevel (AGL) relies on terrain maps or something similar. Since this typeof instrument would reveal nothing about a changing ground level belowan aircraft, any aircraft equipped with it would still require a radaraltimeter for determining AGL on instrument approaches that requiresuch.

Of course, the present invention has additional uses that are notdiscussed in the embodiments above. The present invention has beendescribed in terms of specific embodiments incorporating details tofacilitate the understanding of the principles of construction andoperation of the invention. As such, references herein to specificembodiments and details thereof are not intended to limit the scope ofthe claims appended hereto. It will be apparent that those skilled inthe art that modifications can be made to the embodiments chosen forillustration without departing from the spirit and scope of theinvention.

We claim:
 1. A communication system for a vehicle, comprising: a. anabsolute deceleration detector including an accelerometer, a gyroscopeconfigured to sense an inclination of a movement vector relative to thegravitational acceleration, and a control logic and configured todetermine an absolute deceleration status of the vehicle; b. a brakingsystem engagement detector to detect a braking status of the vehicle; c.an alerting device capable of signaling other drivers of a decelerationcondition of the vehicle; and d. a control device coupled to theabsolute deceleration detector, the braking system engagement detector,and the alerting device, wherein the deceleration detector sends signalsto the control device and the control device operates the alertingdevice in a manner dependent on the absolute deceleration status of thevehicle.
 2. The communication system of claim 1, wherein the alertingdevice comprises lamps on the vehicle that are capable of flashing. 3.The communication system of claim 2, wherein the lamps are capable offlashing only at a constant rate.
 4. The communication system of claim2, wherein the lamps are capable of flashing at a variable rate, andfurther wherein the control device is configured to flash the lamps at arate correlated to a rate of deceleration.
 5. The communication systemof claim 2, wherein the lamps are one of the following: conventionalsignaling lamps and conventional brake lamps.
 6. The communicationsystem of claim 5, wherein the control device further comprises acontrol system for the conventional brake lamp system, whereby thecommunication system is an integrated control and circuitry system forall brake lamps.
 7. The communication system of claim 5, wherein theexisting control system for the conventional brake lamp system issubstantially unmodified, and wherein the control device communicateswith the conventional brake lamp system in a substantially separatemanner.
 8. The communication system of claim 5, wherein the controldevice is an addition to a control system for the conventional brakelamp system.
 9. The communication system of claim 2, wherein the lampsare in addition to conventional brake lamps and conventional signalinglamps.
 10. The communication system of claim 1, wherein the controldevice receives signals from the deceleration detector, a throttleengagement detector, and the braking system engagement detector incycles.
 11. The communication system of claim 1, further comprising aninput device coupled to the control device.
 12. The communication systemof claim 11, wherein the input device comprises a throttle engagementdetector configured to relay a throttle status to the control device.13. The communication system of claim 11, wherein the input devicecomprises a clutch engagement detector configured to relay a clutchstatus to the control device.
 14. The communication system of claim 1,wherein once the braking system is engaged, a conventional brake lampsystem is activated and the communication system is de-activated. 15.The communication system of claim 14, wherein once the braking system isdisengaged, the communication system is re-activated.
 16. Acommunication system for a vehicle, comprising: a. an absolutedeceleration detector including an accelerometer, a gyroscope configuredto sense an inclination of a movement vector relative to thegravitational acceleration, and a control logic and configured todetermine an absolute deceleration status of the vehicle; b. an alertingdevice capable of signaling other drivers of a deceleration condition ofthe vehicle; and c. a control device coupled to the absolutedeceleration detector and the alerting device, wherein the decelerationdetector sends signals to the control device and the control deviceoperates the alerting device in a manner dependent on the absolutedeceleration status of the vehicle.
 17. The communication system ofclaim 16, wherein the alerting device comprises lamps on the vehiclethat are capable of flashing.
 18. The communication system of claim 17,wherein the lamps are capable of flashing only at a constant rate. 19.The communication system of claim 17, wherein the lamps are capable offlashing at a variable rate, and further wherein the control device isconfigured to flash the lamps at a rate correlated to a rate ofdeceleration.
 20. The communication system of claim 16, furthercomprising an input device coupled to the control device.
 21. Thecommunication system of claim 20, wherein the input device comprises athrottle engagement detector configured to relay a throttle status tothe control device.
 22. The communication system of claim 20, whereinthe input device comprises a clutch engagement detector configured torelay a clutch status to the control device.
 23. A communication systemfor a vehicle, comprising: a. an absolute deceleration detectorincluding an accelerometer, a gyroscope configured to sense aninclination of a movement vector relative to the gravitationalacceleration, and a control logic and configured to determine anabsolute deceleration status of the vehicle; b. an alerting devicecapable of signaling other drivers of a deceleration condition of thevehicle, wherein the alerting device comprises lamps on the vehicle thatare capable of flashing; c. a control device coupled to the absolutedeceleration detector and the alerting device, wherein the decelerationdetector sends signals to the control device and the control deviceoperates the alerting device in a manner dependent on the absolutedeceleration status of the vehicle; and d. an input device coupled tothe control device.
 24. The communication system of claim 23, whereinthe lamps are capable of flashing only at a constant rate.
 25. Thecommunication system of claim 23, wherein the lamps are capable offlashing at a variable rate, and further wherein the control device isconfigured to flash the lamps at a rate correlated to a rate ofdeceleration.
 26. The communication system of claim 23, wherein theinput device comprises a throttle engagement detector configured torelay a throttle status to the control device.
 27. The communicationsystem of claim 23, wherein the input device comprises a clutchengagement detector configured to relay a clutch status to the controldevice.
 28. A communication system for a vehicle, comprising: a. anabsolute deceleration detector including an accelerometer, a gyroscopeconfigured to sense an inclination of a movement vector relative to thegravitational acceleration, and a control logic and configured todetermine an absolute deceleration status of the vehicle; b. a brakingsystem engagement detector to detect a braking status of the vehicle; c.an alerting device capable of signaling other drivers of a decelerationcondition of the vehicle; and d. a control device coupled to theabsolute deceleration detector, the braking system engagement detector,and the alerting device, wherein the deceleration detector sends signalsto the control device and the control device operates the alertingdevice in a manner dependent on the absolute deceleration status of thevehicle wherein the control logic uses the inclination of movementvector to determine the absolute deceleration status.
 29. Acommunication system for a vehicle, comprising: a. an absolutedeceleration detector including: i. an accelerometer for determining anacceleration of the vehicle; ii. a gyroscope for determining a deviationfrom a plane perpendicular to earth's gravity, wherein an absolutedeceleration of the vehicle is determined based on a signal from theaccelerometer and a signal from the gyroscope; b. a braking systemengagement detector to detect a braking status of the vehicle; c. analerting device capable of signaling other drivers of a decelerationcondition of the vehicle; and d. a control device coupled to theabsolute deceleration detector, the braking system engagement detector,and the alerting device, wherein the deceleration detector sends signalsto the control device and the control device operates the alertingdevice in a manner dependent on the absolute deceleration status of thevehicle.